Gustatory response profiles for amino acids, glycinebetaine, and nucleotides in several marine teleosts

The gustatory sensitivity of five species of marine teleosts, the aigo rabbitfish Siganus fuscescens, isaki grunt Parapristipoma trilineatum, kampachi amberjack Seriola dumerili, maaji jack mackerel Trachurus japonicus, and masaba chub mackerel Scomber japonicus to amino acids, glycinebetaine and nucleotides was studied by recordsng the neural responses from the facial nerveinnervating the anterior palate. The palatal receptors of all of the five species of fish were responsive to amino acids. Their sensitivity to individual amino acids differed from species to species. At a concentration of 10-4M, the taste receptors of the aigo and isaki responded to the majority of the twenty amino acids tested, while those of the other three species were responsive only to a few. The best five amino acidsin stimulatory effectiveness at 10-4M for the aigo and for the isaki were, in order of effectiveness, serine>proline>alanine>glutamic acid>threonine, and proline>glycine>tryptophan>alanine>serine, respectively, based on 4 to 9 specimens. Those for the kampachi, maaji and masaba at 10-2M were proline>tryptophan>alanine>arginine>cysteine, proline=arginine>asparagine>alanine>methionine, and valine>cysteine>alanine>threonine>serine, respectively, based on 4 to 10 specimens. The taste receptors of all species of fish, except the masaba, were responsive to glycinebetaine at 10-4M. Those of all species fish, except the aigo, were also responsive to nucleotides at 10-4M. Of the nucleotides tested at 10-4M, UMP appeared to be the most effective in each species. In all species, except the masaba, the lowest of the thresholds for the chemicals tested in the present study was for proline, being 10-8-10-6M depending on the species of fish, The masaba was most sensitive to leucine among the amino acids tested, with a threshold of around 10-6-10-5M.